He became emotional as he said, "I swore when I took the job I would never allow any of these kids to become a statistic for me." He admitted to Sawyer that he no longer has a young man's steel for wars that seem to never end.

He writes a personal note to the family of every soldier who dies under his command. Gates knows exactly how many soldiers he has lost over his tenure, "as of yesterday, 1,255 [killed], and about 11,000 wounded," he told Sawyer.

"I go to the hospitals, I go to Arlington. I see their families, so I feel the human cost. And that's why I told somebody the other day maybe it is time for me to leave because these things have begun to weigh on me in a way that maybe I'm not as useful as I used to be."

When asked if he believed he had become too cautious for the job, he replied, "yeah." It's time, he added, to step down.

Gates has served eight presidents since beginning his career with the CIA in 1966 as a fresh-faced 23-year-old.

"Over years, I would still pinch myself. I came from a family of modest means. My brother and I are the first college graduates in our family's history," Gates told Diane Sawyer.

Secretary Gates has received many awards over his career, including the National Security Medal, the Presidential Citizens Medal, the National Intelligence Distinguished Service Medal - twice, and has three times received CIA's highest award, the Distinguished Intelligence Medal.

Gates is also the only Secretary of Defense in U.S. history to remain in office during the transition from one president to another, from President George W. Bush's tenure into the term of President Barack Obama.

Although his mother is still roaring away at the age of 92, Gates told Sawyer he regrets that his father, a former auto parts salesman, never got to see his success.

"That's one of the few regrets that I have. My dad did not live to see me become director of the C.I.A., or the president of Texas A&M, or secretary of defense. But our family is confident he's looking down and has seen it from a different perspective. But I miss that."

Gates is the only career officer in the history of the CIA to rise from entry-level employee to director.